Why? It didn't exist. Many tools exist for the 16-bit Sonic the Hedgehog, but I belong to the small, quiet group who will always prefer the 8-Bit Sonic 1; for what it lacked in big 16-bit graphics they made up with extra game-play, charm and memorable music. It surprised me that a level editor didn't already exist when there are so many for 16-bit Sonic.

This has been a highly technical, very difficult project to undertake. The 8-bit ROM is largely undocumented and working with the Master System data, compression and graphics with Visual Basic 6 has been a slow and methodical processes.

- To be an end-to-end visual editing tool for the ROM, exposing as many aspects as possible, not limited to: editing the palettes, sprite art, title / game over &c. screens / credits text
- To understand and document the original ROM
- To enable creativity in the community

Nowhere just yet, I'm still at a prototype stage right now. I can import the graphics and level data from the original ROM, manipulate the level layout and export to a new, playable ROM but there's still a very large amount of work needed to turn this into a usable product.

For the moment I won't be providing binaries or sources unless to anybody who can genuinely help with the coding / ROM decompiling & documentation.
The source code is now available here: https://github.com/Kroc/MaSS1VE

Updates will be posted here, so you can follow the news and be first to know of a release by subscribing to this thread.

If you're Googling and finding this thread, since you too are looking for a Sonic 1 Master System level editor, then I want to get it out to you as soon as possible, but help is needed:

There is no room in the 256 KB ROM to allow much (if any) editing of the graphics. Changes to the graphics might decrease the compression ratio causing the graphics to run out of ROM space. The solution is to port the original ROM to a 512 KB ROM. This involves editing the z80 assembly code so that the level data and graphics can be moved to different ROM banks where they will have more space to grow. If you can dabble with z80 assembly then you can help.